Re: Patch: Dwarf2 reader -vs- DW_OP_piece

Jim Blandy
2002-02-21T22:09:45Z

Can you explain what sorts of location expressions this is supposed to
help GDB handle?

Tom Tromey <tromey@redhat.com> writes:

> I just submitted a change that changes gcc's Dwarf-2 output.
> It hasn't been approved yet, but of course I'm hoping it will be.
> With this change gcc will now generate DW_OP_piece when a value spans
> multiple registers.
>
> I came up with a somewhat hacky gdb patch to ignore DW_OP_piece.
>
> I'm hoping this patch is just a stopgap until someone adds real
> Dwarf-2 location expression support to gdb.
>
> Ok?
>
> Tom
>
>
> Index: ChangeLog
> from Tom Tromey <tromey@redhat.com>
>
> * dwarf2read.c (decode_locdesc): Recognize DW_OP_piece.
>
> Index: dwarf2read.c
> ===================================================================
> RCS file: /cvs/src/src/gdb/dwarf2read.c,v
> retrieving revision 1.48
> diff -u -r1.48 dwarf2read.c
> --- dwarf2read.c 2002/02/15 22:42:33 1.48
> +++ dwarf2read.c 2002/02/21 18:49:43
> @@ -5808,6 +5808,7 @@
> int stacki;
> unsigned int bytes_read, unsnd;
> unsigned char op;
> + int last_was_piece = 0;
>
> i = 0;
> stacki = 0;
> @@ -5891,8 +5892,13 @@
> case DW_OP_reg29:
> case DW_OP_reg30:
> case DW_OP_reg31:
> - isreg = 1;
> - stack[++stacki] = op - DW_OP_reg0;
> + if (last_was_piece)
> + last_was_piece = 0;
> + else
> + {
> + isreg = 1;
> + stack[++stacki] = op - DW_OP_reg0;
> + }
> break;
>
> case DW_OP_regx:
> @@ -6043,6 +6049,14 @@
> this using GDB's address_class enum. */
> if (i < size)
> complain (&dwarf2_complex_location_expr);
> + break;
> +
> + case DW_OP_piece:
> + /* For now we essentially ignore this. We assume it only
> + occurs when a value spans multiple registers. */
> + read_unsigned_leb128 (NULL, (data + i), &bytes_read);
> + i += bytes_read;
> + last_was_piece = 1;
> break;
>